The project "Longitudinal studies in autism spectrum disorder" consists of longitudinal evaluation of two cohorts of consecutive referrals of two year olds for autism (110 and 83 children), a collaborative cohort of 40 children with disintegrative disorder, as well as a developmentally delayed non-autism comparison group of 21 children in North Carolina and Chicago. The focus is on the divergence of language acquisition, its correlates and trajectories from early preschool to mid school age. Describing and accounting for the wide divergence in the acquisition of expressive and receptive language in autism spectrum disorders is important because of the possibility that severity of language delay/nonverbal communication may be a separate though related factor from the primary social cognitive deficits in autism. Classification studies, particularly concerning Asperger's disorder suggest that while language delay is typically associated with autistic spectrum disorder, it is not necessarily a defining factor. Recent evidence from family and other longitudinal studies indicate that language delay may have somewhat different biological associations than autism-specific social and behavior deficits. In addition, because expressive language skills by school age are the best predictor of outcome within the disorder of autism, understanding the trajectories of children who do and do not acquire fluent speech has direct implication for clinical services. The North Carolina cohort has been evaluated at ages 2, 3 and 4-5. The proposal is to follow them at age 9. Based on clinical diagnoses at age 4- 5 for 128 of the original 131 children, there are 67 children with autism, 30 children with pervasive developmental disorder, not otherwise specified and 31 children with non-spectrum developmental delays. Observation at age 9 will allow further differentiation of language outcome, particularly use of expressive language, measurement of beginning academic achievement, the opportunity to attempt to characterize behavior problems and "co- morbidity" of aggression and attention deficit, measurement of burden on family end better understanding of independent adaptive functioning and social functioning. In Chicago, 83 children referred for autism at ages 2 and 3 will be evaluated at ages 5 and 8-9. The cohort will provide the opportunity to replicate the relationship between early and later diagnosis seen in the North Carolina subjects, increase the sample in order to study divergent outcome, add a focus on children with PD-NOS and allow prelimInary analyses of the effect of services for a selected number of children. A similar protocol will be followed for the disintegrative disorder children. The emphasis is not on subset but rather broader consideration of variability within the phenotype. Some mechanism must be generating the heterogeneity that clearly occurs in association with autism spectrum disorders. The purpose of this project is to characterize dimensions of significance in development within autism spectrum disorder that can be related to neurobiological data, in particular molecular and family genetics, and to better understand this heterogeneity.